Listen to Robert Emmerich introduce The Big Apple, a hit song from 1937. Music written by Bob and performed by Tommy Dorsey's Clambake Seven with Bob on piano. Lyrics written by Buddy Bernier and sung by Edythe Wright. Audio provided by Dorothy Emmerich.

"A fire hydrant has H2O (water) on the inside and K9P (canine pee) on the outside” is a joke that has been printed in several joke books. “If you find H20 inside a fire hydrant, what do you find outside? K9P” was cited in print in 1989.

January 2001, VFW (Veterans of Foreign Wars Magazine), “Jest a Minute,” pg. 50, col. 1:
I was asked what is the chemical symbol for water inside a fire hydrant. I said, “H20.” Then I was asked what is the chemical symbol for water outside a fire hydrant. I said, “K9P.”
Jim Tolnay, Corvallis, Ore.

Google BooksA Prairie Home Companion
Pretty Good Joke Book
Introduced by Garrison Keillor
Minneapolis, MN: HighBridge
2003
Pg. 20:
If H20 is on the inside of a fire hydrant, what is on the outside?
K9P.

Twitter
Sam C
‏@Samography
ori asked for a tweet: If H2O is on the inside of a fire hydrant, what’s on the outside? K9P, of course!
5:04 PM - 31 Jul 2007

Google BooksJokes for Blokes:
The Ultimate Book of Jokes Not Suitable for Mixed Company
By Llewellyn Dowd and Phil McCracken
New York, NY: Ebury Press
2011
Pg. 161:
If there is H20 on the inside of a fire hydrant, what’s on the outside?
K9P.

Google BooksExtremely Embarrassing Dad Jokes:
Because Dads Don’t Know When to Stop
By Ian Allen
New York, NY: Pavilion Books
2015
Pg. ?:
If a fire hydrant has H20 on the inside, what does it have on the outside?
K9P.